From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:45651) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UQJ1F-0004vF-UI for qemu-devel@nongnu.org; Thu, 11 Apr 2013 11:02:36 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UQJ19-0002BV-Qx for qemu-devel@nongnu.org; Thu, 11 Apr 2013 11:02:33 -0400 Received: from mx1.redhat.com ([209.132.183.28]:2612) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UQJ19-0002BO-Bw for qemu-devel@nongnu.org; Thu, 11 Apr 2013 11:02:27 -0400 Date: Thu, 11 Apr 2013 18:01:37 +0300 From: "Michael S. Tsirkin" Message-ID: <20130411150137.GB2280@redhat.com> References: <1365632901-15470-1-git-send-email-mrhines@linux.vnet.ibm.com> <1365632901-15470-11-git-send-email-mrhines@linux.vnet.ibm.com> <20130411073843.GB19601@redhat.com> <51667FEE.903@redhat.com> <5166B9A9.9070904@linux.vnet.ibm.com> <5166C59A.4010904@redhat.com> <5166CF56.2060105@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5166CF56.2060105@linux.vnet.ibm.com> Subject: Re: [Qemu-devel] [RFC PATCH RDMA support v1: 10/13] introduce new command migrate_check_for_zero List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael R. Hines" Cc: aliguori@us.ibm.com, qemu-devel@nongnu.org, owasserm@redhat.com, abali@us.ibm.com, mrhines@us.ibm.com, gokul@us.ibm.com, Paolo Bonzini On Thu, Apr 11, 2013 at 10:57:26AM -0400, Michael R. Hines wrote: > We have hardware already with front side bus speeds of 13 GB/s. > > We also already have 5 GB/s RDMA hardware, and we will likely > have even faster RDMA hardware in the future. > > This analysis is not factoring into account the cycles it takes to > map the pages before they are checked for duplicate bytes, > regardless whether or not very little of the page is actually > cached on the processor. > > This analysis is also not taking into account the possibility that the > VM may be CPU-bound at the same time that QEMU is competing > to execute is_dup_page(). > > Thus, as you mentioned, a worst-case 5 GB/s memory bandwidth > for is_dup_page() could be very easily reached given the right > conditions - and we do have many workloads both HPC and Multi-tier > which can easily cause QEMU's zero scanning performance to suffer. > > - Michael Well, then you can make is_dup_page faster e.g. using the pagemap trick as we discussed earlier. Why does management need a "go fast" option? Just make it go fast... -- MST